Question

我将firebase_messaging 6.0.9与flutter 1.12.13一起使用。在仓库的自述文件中：https://pub.dev/packages/firebase_messaging#-readme-tab-表示将onBackgroudMessage回调声明为静态或顶级方法。我做了，但是当此回调调用非静态方法时，它不起作用。以下示例通过单例类对此进行了演示：

class NotificationService {

  static NotificationService _instance;

  final FirebaseMessaging _firebase;

  static NotificationService get instance => _instance;

  NotificationService._internal() : this._firebase = FirebaseMessaging();

  factory NotificationService() {
    if (_instance == null) {
      _instance = NotificationService._internal();
      _instance._firebase.configure(
          onBackgroundMessage: NotificationService.staticHandler
      );
    }

    return _instance;
  }

  static Future<dynamic> staticHandler(Map<String, dynamic> msg) {
    print("Static Func >>> $msg"); // Successfully prints
    return NotificationService.instance.instanceFunc(msg); // Fails here, complaining that it's being invoked on null.
  }

  Future<dynamic> instanceFunc(Map<String, dynamic> msg) {
    print("Instance Func >>> $msg");
  }

  void myVarFunc() {
    print("This is my var func");
  }
}

在main.dart中，通知服务工厂构造函数称为：

import 'package:myProject/services/notification/notification_service.dart';

run(MyApp());

class MyApp extends StatelessWidget {
   final NotificationService _ns = NotificationService();
   NotificationService.instance.myVarFunc(); // Prints successfully.
   .......
   .......
   .......
}

instanceFunc的调用失败，表示它在null上被调用。以下是日志：

I/flutter ( 6935): Static Func >>> {data: {title: Title_is_here, message: Message_is_here}}
I/flutter ( 6935): Unable to handle incoming background message.
I/flutter ( 6935): NoSuchMethodError: The method 'instanceFunc' was called on null.
I/flutter ( 6935): Receiver: null
I/flutter ( 6935): Tried calling: instanceFunc(_LinkedHashMap len:1)

我不太确定这是否是处理这种情况的正确方法。由于我是Dart和Flutter的新手，因此我的知识非常有限。我不能声明所有事物都是静态的并且可以正常工作，那不是IMO的好设计。我可能在这里错过了一些东西。

Answer 1

出于某些原因，无法在onBackgroundMessage上获得回调：-

onBackgroundMessage在iOS上不起作用，因此您必须实施平台检查

例如：-

    _firebaseMessaging.configure(
      onMessage: (Map<String, dynamic> message) async {
        printDebug("onMessage foreground: $message");
      },
      onBackgroundMessage: Platform.isIOS ? null : _myBackgroundMessageHandler,
      onLaunch: (Map<String, dynamic> message) async {
        printDebug("onLaunch Kill: $message");
      },
      onResume: (Map<String, dynamic> message) async {
        print("onResume Background: $message");
      },
    );
    static Future<dynamic> _myBackgroundMessageHandler(
      Map<String, dynamic> message) async {
    print("onBackgroundMessage: $message");
    return Future<void>.value();
   }

并且您必须确保Notification有效负载中不包含通知密钥，因为如果有效负载中存在通知密钥，则通知将直接由系统处理。因此，您必须从有效负载中删除通知键，才能在onBackgroundMessage上进行回调。

注意：-如果删除通知键，则通知未在系统通知托盘中呈现。为此，您可以本地通知。

Flutter FCM onBackgroundMessage不适用于嵌套的非静态方法调用

1 个答案: